Welcome to the forum,
Congrats on the GMC.
Post the engine number that is pressed into the boss/ledge n the block, to the rear of where the distributor enters the block. Someone will be able to tell you if its a Chevy/GMC engine and the size of the engine. If the engine is original and standard, it would most likely be a GMC 228, if your truck is a USA GMC. If if is a Canadian GMC, I think that the engine might have been either a GMC or a Chevrolet engine (someone will correct/clarify this, if it is incorrect).
In all years, Chevrolet Advance-Design trucks were the truck sales leader in the USA (
sales back to 1927 ).
If you have trouble finding parts locally,
you can find many part numbers here. (it takes getting use to their catalog)
Tim
